In recent years, as vehicle lamps such as vehicle headlights, in order to reduce an energy consumption of a light source, products using light-emitting diodes (LED) or laser diodes (LD) have been proposed, and some of the products are practically used. In particular, since an LD light source has high phototransformation efficiency and a small light-emitting area, the LD light source is advantageous in terms of a reduction in size of a lamp. A vehicle lamp using an LD light source is configured to cause an LD element to irradiate excitation light (for example, blue laser light) to a phosphor and to mix light (for example, yellow light) generated by exciting the phosphor with the excitation light in color so as to emit visible light (for example, white light). For example, PTL 1 describes an illumination device including an excitation light source emitting excitation light having an oscillation wavelength in a blue-violet region, a light-emitting unit which receives the excitation light emitted from the excitation light source to emit light, and a transmitting filter which blocks a coherent component included in the excitation light and transmits an incoherent component thereof.